Mobile communications system, methods, controller, relay node and communications terminal

ABSTRACT

A controller is configured to control a first of plural relay nodes to transmit signals representing data to one of communications terminals received from a base station or to receive signals representing data from a communications terminal for transmission to the base station, wherein, upon first predetermined conditions being met, to control a second of the plurality of relay nodes to transmit signals representing the data to the communications terminal received from the base station or to receive signals representing the data from the communications terminal for transmission to the base station, and to control the communications terminal to transmit a first signal representing at least a first part of the data to the first relay node for transmission to the base station, and to transmit a second signal representing at least a second part of the data to the second relay node for transmission to the base station.

TECHNICAL FIELD OF THE DISCLOSURE

The present disclosure relates to mobile communications networks,methods, relay nodes and communications terminals, and more specificallyto providing an arrangement in which a communications terminalcommunicates with a base station via a relay node.

Embodiments of the present technique can provide methods ofcommunicating data in a small cell environment where relay nodes may beused.

BACKGROUND OF THE DISCLOSURE

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentdisclosure.

Third and fourth generation mobile telecommunication systems, such asthose based on the 3GPP defined UMTS and Long Term Evolution (LTE)architecture are able to support more sophisticated services than simplevoice and messaging services offered by previous generations of mobiletelecommunication systems. For example, with the improved radiointerface and enhanced data rates provided by LTE systems, a user isable to enjoy high data rate applications such as mobile video streamingand mobile video conferencing that would previously only have beenavailable via a fixed line data connection. The demand to deploy thirdand fourth generation networks is therefore strong and the coverage areaof these networks, i.e. geographic locations where access to thenetworks is possible, is expected to increase rapidly.

The anticipated widespread deployment of third and fourth generationnetworks has led to the parallel development of a number of newinfrastructure architectures involving a variety of classes of devices,of wireless access point units and of applications which may requiredifferent data rates, coverage areas or transmission powers. Unlike aconventional third or fourth generation communications device such as asmartphone, an MTC-type terminal is preferably relatively simple andinexpensive, having a reduced capability. Examples of recentdevelopments include so-called machine type communication (MTC)applications, which are typified by semi-autonomous or autonomouswireless communication devices (i.e. MTC devices) communicating smallamounts of data on a relatively infrequent basis. Examples includeso-called smart meters which, for example, are located in a customer'shouse and periodically transmit information back to a central MTC serverdata relating to the customers consumption of a utility such as gas,water, electricity and so on. Other examples include relay nodes whichprovide assistance to local terminal communicating with a base station.

Whilst it can be convenient to have different systems addressingdifferent needs from different mobile network users, the additions ofnew infrastructure and new services can also create an infrastructureproblem, which is not desirable in a mobile network.

With the continuous growth in data transmitted in mobile networks,continually increasing network capacity comparatively is a problem facedby the industry. There are three parameters which can be changed inorder to increase Radio Access network capacity: higher spectralefficiency, more radio spectrum and denser cell layout. The two formerof these have limitations on the expected gains over today's LTE, andcertainly improvements on the order of magnitude or more are notpossible. Thus, in order to meet the stated 1000× capacity targets,small cells are getting a lot of attention [1].

SUMMARY OF THE DISCLOSURE

According to an example embodiment of the present disclosure there isprovided a mobile communications system comprising a base station, whichis operatively coupled to a controller. The base station includes atransmitter and a receiver, the transmitter being configured to transmitsignals via a wireless access interface to a plurality of relay nodesand to one or more communications terminals, and the receiver beingconfigured to receive signals via the wireless access interface from theplurality of relay nodes and from the one or more communicationsterminals. The controller is configured to control a first relay node ofthe plurality relay nodes to transmit signals representing the data toone of the communications terminals for transmission to the base stationor to receive signals representing the data from the communicationsterminal for transmission to the base station, wherein, upon firstpredetermined conditions being met, to control a second relay node ofthe plurality of relay nodes to transmit signals representing the datato the communications terminal received from the base station or toreceive signals representing the data from the communications terminalfor transmission to the base station, and to control the communicationsterminal to transmit a first signal representing at least a first partof the data to the first relay node for transmission to the basestation, and to transmit a second signal representing at least a secondpart of the data to the second relay node for transmission to the basestation.

When a communications terminal communicates via a relay node to aneNodeB, there are several potential issues. The first of these is thatthe communications terminal may have a poor connection to that relaynode, or the relay node may be consuming too much power or dealing withtoo much traffic. The relay node is likely to be capacity limited, andif the amount of traffic being communicated between the communicationsterminal and the eNodeB via the relay node is greater than the relaynode's capacity, it may become a bottleneck to the system, therebyincreasing latency and delays, as well as wasting power and causing themobile communications system to be more inefficient in general. Theprovision of a second relay node in order to alleviate the traffic orpower load on a capacity constrained relay node, or a relay node whichis communicating with a communications device via an instable or lowquality channel, may provide a solution to some or all of these issues.

Embodiments of the present disclosure, then, can increase acommunications bandwidth available to a communications terminal, forexample where a relatively high amount of data needs to be communicatedby a communications terminal to an eNodeB, or where the communicationsterminal may be out of coverage of the eNodeB. This may be achievedthrough the employment of a dual connection, with two relay nodesrelaying signals between the communications terminal and the eNodeB.This in itself has its own challenges to overcome, and the presentdisclosure also reduces a likelihood or avoids a conflict incommunications between the communications terminal and a relay node whenmore than one relay node is used.

Accordingly the the first and second relay nodes may be arranged to forma dual connection between the communications terminal and the basestation such that the capacity of the mobile communications system isincreased, and the power consumed by a relay node than if it wasrelaying signals between the communications terminal and base stationalone would be a lot lower. Further, an out-of-coverage communicationsterminal may not be able to communicate directly with the base station,and therefore relies on an associated relay node to relaycommunications. Should the radio communications channel between thecommunications terminal and the relay node be of a low quality orstability, communications will become severely affected. A second relaynode, with which the communications terminal shares a better quality,more stable channel, may be required to be activated, so that it mayrelay signals between the base station and the out of coveragecommunications terminal.

Further, the traffic load of a relay node operating alone between acommunications terminal and a base station may be greater than itscapacity, thereby causing the relay node to become a bottleneck to themobile communications system. In this case, latency would be increasedand the mobile communications system would suffer delays, which would beproblematic in time-critical scenarios such as video streaming etc. Inorder to reduce this latency, a second relay node could be activated toprovide a dual connection implementation where the traffic load of asingle relay node is alleviated.

Various further aspects and features of the present technique aredefined in the appended claims, which include a mobile communicationsnetwork comprising a base station, one or more relay nodes and one ormore communications terminals, a method of operating a base station as anetwork controller, a base station forming part of a mobilecommunications network, circuitry for a base station forming part of amobile communications network, a relay node forming part of a mobilecommunications network, circuitry for a relay node forming part of amobile communications network, a communications terminal forming part ofa mobile communications network, and circuitry for a communicationsterminal forming part of a mobile communications network.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings wherein likereference numerals designate identical or corresponding parts throughoutthe several views, and wherein:

FIG. 1 provides a schematic diagram of a mobile communications systemaccording to an example of an LTE standard;

FIG. 2 schematically illustrates an example of a small cell environment;

FIG. 3 illustrates another example of a small cell environment;

FIG. 4 illustrates an example system for communicating with at least aterminal in a heterogeneous network;

FIG. 5 illustrates an example mobile communications system in accordancewith the present technique;

FIG. 6 illustrates an example of carrier aggregation as an examplemethod of implementing a dual relay connection in accordance with thepresent technique;

FIG. 7 illustrates an example of separate communications resource poolsas an example method of implementing a dual relay connection inaccordance with the present technique;

FIG. 8 illustrates an example of the activation of a dual relayconnection by a base station in accordance with the present technique;

FIG. 9 illustrates the concept of the deactivation of a dual relayconnection by a base station in accordance with the present technique;

FIG. 10 illustrates an example of the activation of a dual relayconnection by a communications terminal in accordance with the presenttechnique; and

FIG. 11 illustrates the concept of the deactivation of a dual relayconnection by a communications terminal in accordance with the presenttechnique.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Hereinafter preferred embodiments of the present technique will bedescribed in detail with reference to the appended drawings. Note that,in this specification and appended drawings, structural elements thathave substantially the same function and structure are denoted with thesame reference numerals, and repeated explanation of these structuralelements is omitted.

FIG. 1 provides a schematic diagram illustrating some basicfunctionality of a conventional mobile telecommunications network, usingfor example a 3GPP defined UMTS and/or Long Term Evolution (LTE)architecture. The mobile telecommunications network/system 100 of FIG. 1operates in accordance with LTE principles and which may be adapted toimplement embodiments of the disclosure as described further below.Various elements of FIG. 1 and their respective modes of operation arewell-known and defined in the relevant standards administered by the3GPP (RTM) body, and also described in many books on the subject, forexample, Holma H. and Toskala A [2]. It will be appreciated thatoperational aspects of the telecommunications network which are notspecifically described below may be implemented in accordance with anyknown techniques, for example according to the relevant standards.

The network 100 includes a plurality of base stations 101 connected to acore network 102. Each base station provides a coverage area 103 (i.e. acell) within which data can be communicated to and from terminal devices104. Data is transmitted from base stations 101 to terminal devices 104within their respective coverage areas 103 via a radio downlink. Data istransmitted from terminal devices 104 to the base stations 101 via aradio uplink. The uplink and downlink communications are made usingradio resources that are licensed for use by the operator of the network100. The core network 102 routes data to and from the terminal devices104 via the respective base stations 101 and provides functions such asauthentication, mobility management, charging and so on. The terminaldevices may also be referred to as mobile stations, user equipment (UE),user terminal, mobile terminal, mobile device, terminal, mobile radio,and so forth. Base stations may also be referred to as transceiverstations/nodeBs/e-nodeBs/eNodeB, and so forth.

Mobile telecommunications systems such as those arranged in accordancewith the 3GPP defined Long Term Evolution (LTE) architecture use anorthogonal frequency division multiplex (OFDM) based interface for theradio downlink (so-called OFDMA) and the radio uplink (so-calledSC-FDMA).

The base stations 101 of FIG. 1 may be realised as any type of evolvedNode B (eNodeB) such as a macro eNodeB and a small eNodeB. The smalleNodeB may be an eNodeB such as a pico eNodeB, a micro eNodeB, and ahome (femto) eNodeB that covers a cell smaller than a macro cell.Instead, the base station 101 may be realized as any other types of basestations such as a NodeB and a base transceiver station (BTS). The basestation 101 may include a main body (that is also referred to as a basestation apparatus) configured to control radio communication, and one ormore remote radio heads (RRH) disposed in a different place from themain body. In addition, various types of terminals, which will bedescribed below, may each operate as the base station 101 by temporarilyor semi-persistently executing a base station function.

Any of the communications devices 104 may be realized as a mobileterminal such as a smartphone, a tablet personal computer (PC), anotebook PC, a portable game terminal, a portable/dongle type mobilerouter, and a digital camera, or an in-vehicle terminal such as a carnavigation apparatus. The communications device 104 may also be realizedas a terminal (that is also referred to as a machine type communication(MTC) terminal) that performs machine-to-machine (M2M) communication.Furthermore, the terminal apparatus 104 may be a radio communicationmodule (such as an integrated circuit module including a single die)mounted on each of the terminals.

In the present disclosure, a base station providing a small cell isgenerally differentiated from a conventional base station mostly (andsometimes exclusively) in the range provided by the base station. Smallcells include for example the cells also called femtocell, picocell ormicrocell. In other words, small cells can be considered as similar tomacrocells in the channels and features provided to the terminals, butwith the use of less power for base station transmissions, which resultsin a smaller range. A small can therefore be the cell or coverageprovided by a small cell base station. In other examples, the term smallcell can also refer to a component carrier when more than one componentcarrier is available.

FIG. 2 illustrates an example of a small cell environment 200 wherein aplurality of base stations 201 to 204 are operable to communicate withterminals, such as terminal 211. In this example, the terminal 211 is incommunication with base station 201 providing a first small cell but iswithin the range of the small cell for each of base stations 202, 203and 204. As a result, the signals sent by base station 201 to terminal211 can suffer from interference from signals transmitted by basestations 202 to 204. While with conventional macrocell networks the sametype of situation would also be likely, in practice, the mobile operatoris in a position to carry out frequency planning, distributingfrequencies amongst base stations in a static or dynamic manner.Accordingly, the level of interference can be significantly reduced formacrocells. On the other hand, when dealing with a small cell network,there may be a potentially very large number of base stations, eachusing different powers such that network planning becomes much moredifficult, and the complexity also increases with the number of activesmall cells in an area. In particular, if a large number or small cellsare available in an area, it is likely that they will not be able toeach be allocated a different, non-overlapping frequency bands such thattransmissions from different cells would not interfere with each other.Moreover, small cell networks have the additional difficulty that asmall cell may be mobile, i.e. not stationary, while network planningfor a macrocell or legacy femto/picocells was generally based onstationary or fixed base stations. This also increases the complexity oftrying to reduce interference significantly. Of course, interferencebetween small cells can be significant when the number of deployed smallcells increases such that in a dense small cell environment,interference reduction can be challenging. As a result, in the eventthat the interference affects synchronization signals or referencesignals of small cells, terminals may not even be able to discover andconnect to small cells.

An example of a small cell environment 300 is illustrated in FIG. 3,where a macrocell base station 311 is provided in the same area as smallcells provided by a base station 301 in or in the vicinity of abuilding, by a base station 302 in a first lamppost, by a base station303 in a second lamppost, by a base station 305 provided in a bus stopand by a mobile base station 306 provided in a cyclist back-pack. Inthis example, the planning for interference may vary depending ontraffic and on time. For example a cyclist may enter an interferencezone this zone. However, the base station 301, if serving an office, maypotentially only be used during office hours and may be turned offduring the rest of the day or the rest of the week. A variety of basestations may thus be providing a small or macro cell and the basestation may have very different profile regarding time of use, frequencycapabilities, power/range, additional functionalities, etc.

Moreover, mobile networks can also include relay nodes which can furtherincrease the complexity of the mobile system and of the reduction ofinterference in a small cell network. FIG. 4 illustrates an examplesystem 400 for communicating with at least a terminal 431. In thissystem 400, a base station 401 provides a macrocell and six basestations 411 to 416 provide small cell coverage, potentially overlappingwith the coverage of the base station 401. Additionally, three relaynodes 421 to 423 are provided and are operating with base stations 401,414 and 412, respectively. A relay node can generally be defined as awireless radio access point for relaying transmission and which thusdoes not implement all of the functionalities of a base station. It isin general not directly connected to the core network but uses wirelessaccess (inband or outband) for backhaul link to connect with a basestation. In other examples, a backhaul link may also be provided over awired connection. This is in contrast to a small cell base stationwhich, as mentioned above, can generally operate like a base station andis thus connected to the core network, as illustrated by the arrowsbetween the small cell base stations 411 to 416 and the Serving Gateway“S-GW” in FIG. 4. Relay nodes may also send or receive data with theterminals or base stations, forming an ad-hoc network which can also addto the complexity of dealing with interference in an environment asillustrated in FIG. 4.

Relay technologies are known generally to provide an arrangement forreceiving signals from a base station and for retransmitting thereceived signals to a user equipment (UE, a communications terminal) ina mobile communications network, or to receive signals transmitted froma UE for re-transmission to a base station of a mobile communicationsnetwork. The aim of such relay nodes is to try to extend a radiocoverage area provided by a mobile communications network to reachcommunications devices which would otherwise be out of range of themobile communications network or to improve the ratio of successfultransmissions between a terminal and a base station.

If two relay nodes are employed between a UE and a base station, it ispossible to set up a dual connection. This may be advantageous in termsof saving or balancing power consumption between relay nodes.Additionally, traffic may be balanced between relay nodes, and a relaynode at which a large amount of data may be received and transmittedcould avoid becoming a bottleneck for the network, thereby increasinglatency and delays. The overall advantageous effect of employing a dualrelay connection between a UE and a base station then, is to increasethe overall efficiency of the network.

Dual Relay Node Connection

According to an example embodiment of the present disclosure there isprovided a mobile communications system comprising a base station, whichis operatively coupled to a controller. The base station includes atransmitter and a receiver, the transmitter being configured to transmitsignals via a wireless access interface to a plurality of relay nodesand to one or more communications terminals, and the receiver beingconfigured to receive signals via the wireless access interface from theplurality of relay nodes and from the one or more communicationsterminals. The controller is configured to control a first relay node ofthe plurality relay nodes to transmit signals representing the data toone of the communications terminals or to receive signals representingthe data from the communications terminal, wherein, upon firstpredetermined conditions being met, to control a second relay node ofthe plurality of relay nodes to transmit signals representing the datato the communications terminal received from the base station or toreceive signals representing the data from the communications terminalfor transmission to the base station, and to control the communicationsterminal to transmit a first signal representing at least a first partof the data to the first relay node for transmission to the basestation, and to transmit a second signal representing at least a secondpart of the data to the second relay node for transmission to the basestation. FIG. 5 illustrates an example mobile communications system 500in accordance with an arrangement of the present disclosure.

The system comprises an eNodeB 501, which may serve as the networkcontroller, three relay nodes 502, 503 and 504, and two mobilecommunications terminals, or UEs 505 and 506, all of which are served bythe eNodeB 501. The eNodeB comprises a transmitter configured totransmit data across a wireless access interface to the UEs 505 and 506and the relay nodes 502, 503 and 504, and a receiver configured toreceive data from the UEs 505 and 506 and the relay nodes 502, 503 and504 in return.

The UE B 506 is configured to transmit signals representing data 507 tothe eNodeB 501 via the relay node 503. It may later be decided by thenetwork controller, or requested by the UE B 506 that a second relaynode is required to relay some of the traffic from the UE B 506 to theeNodeB 501. In this case, the UE B 506 is considered to transmit a firstsignal 508 representing at least a first part of the data to one relaynode 503, and a second signal 509 representing at least a second part ofthe data to another relay node 502. Both relay nodes 502 and 503 willthen transmit the signals representing a part of the data 508 and 509that they received from the UE B 506 to the eNodeB 501.

There are multiple approaches as to how a dual connection may beimplemented. One such method is the employment of carrier aggregation.At least a part of the data may be modulated with a first carriersignal, and at least part of the data may be modulated with a secondcarrier signal, and these signals may be transmitted independently.

FIG. 6 shows an example of carrier aggregation 600 using separatecarrier signals as an example method of implementing a dual relayconnection in accordance with the present technique. In the first image,a UE 601 transmits signals 606 to and receives signals 606 from a relaynode 603 of a plurality of relay nodes 603, 604 and 605. The signals 606comprise a primary component carrier (PCC) and secondary componentcarrier (SCC). The relay node 603 in turn transmits the same signals 606to and receives the same signals 606 from a base station 602. However,the power consumption at the relay node 603 in this scenario will behigh, and it may be the case that the network decides it is moreefficient to implement a dual connection.

In the case that a dual relay connection is implemented, in the secondimage, a UE 6011 transmits signals 616 to and receives signals 616 fromtwo relay nodes 613 and 615 of a plurality of relay nodes 613, 614 and615. The first relay node 613 relays the PCC signal 617 to the basestation 612, while the second relay node 615 relays the SCC signal 618to the base station 612. In this scenario, less power is consumed byeach of the relay nodes 613 and 615 than if they were not operating witha UE with a dual connection.

FIG. 7 shows an example of separate communications resource pools 700 asan example method of implementing a dual relay connection in accordancewith the present technique. A UE 701 is configured to transmit twosignals, each representing a part of overall data to be transmitted, totwo relay nodes 703 and 704 for transmission to a base station 702. Thetwo signals are transmitted in separate resource pools Tx1 and Tx2. Theresource pools may be separated, for example, in time, or in frequency,etc. The first relay 704 is configured to receive the first signal inthe first resource pool Rx1, and the second relay 703 is configure toreceive the second signal in the second resource pool Rx2. These signalsare then transmitted on to the base station 702 by the relay nodes 703and 704. Each relay node is only configured to monitor signals in theresource pool configured for it, and ignore signals in the resource poolconfigured for the other relay node. For downlink communications, it isnot necessary to worry about the distinction between relay nodes, and soonly one resource pool is required.

In the case of employing separate communications resource pools forimplementing a dual relay node connection, the configuration of theresource pools may be shared. For downlink communications, the relaynodes may configure the transmission (Tx) resource pools, and the UE mayconfigure the receiver (Rx) resource pools. If the uplink traffic loadis high, the configuration of resource pools may also be carried out foruplink communications. In this case, the relay nodes may configure theRx resource pools and the UE may configure the Tx resource pools. Thedrawback of such a configuration is that more communications resourcesare used up, and the UE may consume additional power. However, itprovides the advantageous effects of reducing power consumption andtraffic load for each of the relay nodes, and only one carrier signal isrequired. Appropriately, it is beneficial to deactivate the second relaynode when it is not required in order to save power consumption andcommunications resources.

A further approach as to how a dual connection may be implemented may beto configure the relay nodes with different device-to-device (D2D)identifiers.

In a first example embodiment of the present disclosure, it is theeNodeB, acting as the network controller, which leads the activation anddeactivation of the second relay node. In this first example embodiment,the necessity of the second relay node connection is dependent on thetraffic load. The eNodeB scheduler is aware of the current level oftraffic load (for example, by looking at the buffer sizes), and thisinformation may be used for making the decisions regarding theactivation and deactivation of the second relay node.

FIG. 8 shows how the activation of a dual relay node connection 800 maybe carried out by an eNodeB in accordance with the first exampleembodiment of the present disclosure. Initially, the eNodeB sends acommand to activate the first relay node, so that it may relay signalsbetween the UE and the eNodeB. The first relay node sends a confirmationthat it has received this command, activates and configures the Tx/Rxresource pools, and sends a notice to the UE that it is available as arelay node. Alternatively, the notice to the UE may be provided by theeNodeB. The UE sends a confirmation that it has received this notice,and the first relay node begins transmitting and receiving data messagesfrom the UE and from the eNodeB.

At a point later in time, the eNodeB scheduler may determine that thebuffer status of the first relay node is high, and there is a lot oftraffic being handled by it. Alternatively, the eNodeB scheduler maydetect the high traffic load through a scheduling request. The eNodeBmay then decide that a second relay node should be activated in order toalleviate the high traffic load of the first relay node, and so selectsthe second relay node from among one or more candidate relay nodes. TheeNodeB may then send an activation command to the second relay node, andreceive a confirmation from the second relay node that this has thenbeen received. The second relay node is now activated and may relaysignals between the UE and eNodeB, and the UE is notified of this byeither the second relay node or the eNodeB.

FIG. 9 shows how the deactivation of a dual relay node connection 900may be carried out by an eNodeB in accordance with the first exampleembodiment of the present disclosure. Initially, it is assumed that theeNodeB has already activated a first relay and a second relay node asdescribed with reference to FIG. 8 above, so that both the first relaynode and the second relay node are operating with a dual connection to aUE, relaying signals between the UE and the eNodeB.

At some point, the eNodeB scheduler may determine that the buffer statusof the second relay node is low, and there is a low level of trafficbeing handled by it. Alternatively, the eNodeB scheduler may detect thelow traffic low through a scheduling request. The eNodeB may then decidethat a dual connection is no longer required, and may then send adeactivation command to the second relay node. The second relay node maysend a confirmation message to the eNodeB, at which point it becomesdeactivated. The UE may then be notified of the deactivation by eitherthe second relay node or the eNodeB.

For both the activation and deactivation procedures as described withreference to FIGS. 8 and 9 in accordance with the first exampleembodiment of the present disclosure, the connection between the UE andthe first relay node should be separated from that of the connectionbetween the UE and the second relay node. As described, this may beachieved through a number of methods, including but not limited toemploying a carrier aggregation implementation, separated communicationsresource pools, or different D2D identifiers for each of the first andsecond relay nodes.

For both the activation and deactivation procedures as described withreference to FIGS. 8 and 9 in accordance with the first exampleembodiment of the present disclosure, the example trigger condition usedfor the activation or deactivation of the second relay node is thetraffic load of the relay nodes. There are a number of possible triggerconditions that may be used for the activation or deactivation of asecond relay to form or terminate a dual connection, and these includebut are not limited to the following:

An example trigger condition may be the status of a buffer. The eNodeBscheduler has a perfect knowledge of the buffer status of relay nodesand UEs in the network for downlink communications. In addition, theeNodeB scheduler may know the buffer status of the relay nodes and UEsbased on feedback signalling, e.g. a buffer status report. The bufferstatus as a trigger condition may be handled per channel, per bearer(where it is assumed that one connection between a UE and relay node hasone bearer between the relay node and eNodeB) or per UE. The bufferstatus may also be handled per relay, in terms of aggregated trafficwhich is discussed below.

A second example trigger condition may be the inactivity of traffic.Typically, packet traffic arrives in bursts, and is not transmitted orreceived at a continuous rate. The eNodeB may be equipped with a timerto measure the inactivity of traffic, and when this timer expires, theeNodeB may deactivate the second relay node. Accordingly, in thecontrasting scenario where traffic activity is detected over a period oftime measured by the eNodeB's timer, the eNodeB may activate the secondrelay node. This measurement and timer could be applicable for uplinkand downlink communications separately.

A third example trigger condition may be the power headroom (PHR). TheeNodeB knows the allocated power of the channel or bearer, similarly tological channels (which are determined by the information carried withina physical channel). The power headroom is an indirect indicator of thetraffic load. A small level of power headroom of the first relay node(i.e. the difference between the transmission power available to thefirst relay node and the current amount of power being consumed by thefirst relay node) may be the trigger condition in this case to activatethe second relay node to implement a dual connection. In addition tobeing controlled from the eNodeB side of the communications system, thepower headroom for a relay node or UE may be alternatively reported fromthe relay node or UE it concerns to the eNodeB.

A fourth example trigger condition may be a traffic load trigger, butbased on aggregated traffic among relay nodes and UEs rather than thetraffic load of an individual relay node or UE. The first relay node maytreat the traffic coming through it as having been transmitted by morethan one UE, and has the limitation of maximum throughput between therelay node and eNodeB. In order to avoid becoming a bottleneck to thecommunications system, and thereby increasing latency and delays, thefirst relay node may need to be joined by a second relay node inrelaying signals from the first relay node's serving UE or UEs. Theprocess begins with a new UE becoming associated with the first relaynode, and communicating with it. The eNodeB may estimate the totaltraffic of the first relay node after the new UE has become associatedwith it, and dependent on this traffic, the eNodeB may decide toactivate the second relay node. It is possible, if necessary, for theeNodeB to activate the second relay node for a second UE which has notitself yet activated the second relay node. The eNodeB may then controltraffic, by restricting the level of traffic being communicated via thefirst relay node and offloading some of the traffic to be communicatedvia the second relay node.

A fifth example trigger condition may be the quality of the channel, interms of coverage stability. If the UE faces unstable channel qualitybetween itself and a first relay node with which it is associated, asecond relay node, with which the UE shares a higher quality, morestable channel, may be activated.

In a second example embodiment of the present disclosure, it is the UEwhich leads the activation and deactivation of the second relay node, bydetecting a high or low load of traffic and transmitting requestmessages to the eNodeB for the activation or deactivation of the secondrelay node. In this second example embodiment, the necessity of thesecond relay node connection is dependent on the traffic load. The UEhas a perfect knowledge of the buffer status for uplink communications,so this embodiment of the present disclosure may be advantageous forapplications such as uploading large video files or streaming videoapplications from a camera.

FIG. 10 shows how the activation of a dual relay node connection 1000may be carried out by a UE in accordance with the second exampleembodiment of the present disclosure. Initially, the eNodeB sends acommand to activate the first relay node, so that it may relay signalsbetween the UE and the eNodeB. The first relay node sends a confirmationthat it has received this command, activates and configures the Tx/Rxresource pools, and sends a notice to the UE that it is available as arelay node. Alternatively, the notice to the UE may be provided by theeNodeB. The UE sends a confirmation that it has received this notice,and the first relay node begins transmitting and receiving data messagesfrom the UE and from the eNodeB.

At a point later in time, the UE may determine that the buffer status ofthe first relay node is high, and there is a lot of traffic beinghandled by it. The UE may then decide that a second relay node should beactivated in order to alleviate the high traffic load of the first relaynode, and so sends an activation command to the eNodeB via the firstrelay node. The eNodeB may then send an activation command to the secondrelay node, and receive a confirmation from the second relay node thatthis has then been received. The second relay node is now activated andmay relay signals between the UE and eNodeB, and the UE is notified ofthis by either the second relay node or the eNodeB.

FIG. 11 shows how the deactivation of a dual relay node connection 1100may be carried out by a UE in accordance with the second exampleembodiment of the present disclosure. Initially, it is assumed that theeNodeB has already activated a first relay and a second relay node asdescribed with reference to FIG. 10 above, so that both the first relaynode and the second relay node are operating with a dual connection to aUE, relaying signals between the UE and the eNodeB.

At some point, the UE may detect that the buffer status of the secondrelay node is low, and there is a low level of traffic being handled byit. The UE may then decide that a dual connection is no longer required,and may then send a deactivation command to the eNodeB via the firstrelay node. The second relay node may send a confirmation message to theeNodeB, at which point it becomes deactivated. The UE may then benotified of the deactivation by either the second relay node or theeNodeB.

For both the activation and deactivation procedures as described withreference to FIGS. 10 and 11 in accordance with the second exampleembodiment of the present disclosure, the connection between the UE andthe first relay node should be separated from that of the connectionbetween the UE and the second relay node. As described, this may beachieved through a number of methods, including but not limited toemploying a carrier aggregation implementation, separated communicationsresource pools, or different D2D identifiers for each of the first andsecond relay nodes.

For both the activation and deactivation procedures as described withreference to FIGS. 10 and 11 in accordance with the second exampleembodiment of the present disclosure, the example trigger condition usedfor the activation or deactivation of the second relay node is thetraffic load of the relay nodes. There are a number of possible triggerconditions that may be used for the activation or deactivation of asecond relay to form or terminate a dual connection, as have beendiscussed with regard to the first example embodiment of the presentdisclosure and FIGS. 8 and 9.

A mobile communications system operating in accordance with the presentdisclosure holds a number of advantages. With regard to the scenario inwhich the eNodeB controls the activation and/or deactivation of thesecond relay node, as in the first example embodiment described above,there are several advantages in that: the eNodeB scheduler has a perfectknowledge of the buffer status of traffic for downlink communications,the eNodeB can be aware of the traffic through a relay node not only fora specific UE but for other UEs as well, and therefore can be aware ofthe aggregated traffic through that relay node, and the eNodeB may alsobe in charge of the final decision of the activation of a second relaynode based on comprehensive information. With regard to the scenario inwhich the UE controls the activation and/or deactivation of the secondrelay node, as in the second example embodiment described above, thereare also advantages in that: the UE has a perfect knowledge of thebuffer status of traffic for uplink communications, and the UE knows oris able to measure the internal status of the UE, for example the powerheadroom.

A further advantage held by a mobile communications system operating inaccordance with the present disclosure is that the employment of morethan one relay node between a UE and an eNodeB will result in less powerbeing consumed by each relay node than if they were operatingindividually between the UE and the eNodeB. This is not an overlyadvantageous effect in itself as the overall power consumed is not anylower; indeed it is higher as power is consumed for the establishment ofradio communications links for the second relay node and theconfiguration of separate communications resource pools should that bethe method of relay node separation. However, should the power headroomof the first relay node be very small, to the detriment of theperformance of the mobile communications system, then the employment ofa second relay node becomes advantageous.

An additional advantage based on the above advantage comes about interms of deactivation of the second relay node should the combinedtransmission power consumed by both relay nodes be low enough that thepower headroom for a single relay node would be sufficiently large. Inthis case, when there is no disadvantage to using a single relay nodebetween the UE and eNodeB in terms of power headroom, the UE/relay nodesaving power in terms of the configuration of separate communicationsresource pools and configuration of the second relay node would be anadvantage. Clearly operating two relay nodes in a dual connection willalways be advantageous to the mobile communications system in terms ofcapacity, but not necessarily power. Often it may be a trade off betweenthe two with regard to the activation or deactivation of a second relaynode to implement a dual connection.

A yet further advantage held by a mobile communications system operatingin accordance with the present disclosure is with regard to the trafficbalancing between relay nodes. The eNodeB has information on aggregatedtraffic of relay nodes, which are served by the eNodeB. The eNodeB maydecide to balance the traffic among relays, and activate or deactivatethe second relay node if necessary. This provides the advantageouseffect that the traffic bottlenecking of a specific relay node can beavoided, thereby decreasing latency and delays.

A dual relay node connection could be provided between a UE and aneNodeB if, for example, the capabilities of the relay nodes weredifferent. The first relay node may be, for example, of an MTCcapability, designed to transmit and receive frequent signals of lowpower and bandwidth, while the second relay node may be of a capabilitydesigned for applications such as uploading large video files orstreaming video applications from a camera. It may also be the case thatdifferent UEs or relay nodes support different frequency bands, and asecond relay node may need to be activated to operate in a dualconnection when communicating in that band.

In accordance with the present disclosure, all example embodimentsdescribed are based on a dual connection comprising of a base station oreNodeB, a UE and two relay nodes. However, mobile communications systemsoperating in accordance with the present disclosure are not limited tohaving two relay nodes, or even limited to having a UE operating withtwo relay nodes with a dual connection. It would be perfectly possibleto expand the idea in the same way to operate with a triple relay nodeconnection.

Further, it is not necessary for a UE and a relay node as described tobe distinctly separate entities. A UE operating as a UE to network relayin D2D may have a relay function which can be activated if necessary.Therefore, it is within the scope of the present disclosure for the UEand the relay node to be physically the same product.

In the present disclosure, the term infrastructure unit aims to refer toany network node in the radio access network which can be found on thepart from a source terminal (excluded) to a base station (included). Itis noteworthy that although conventional terminals operating in a legacynetwork are unlikely to be considered as an infrastructure unit, in someexamples, such as in some D2D cases, a terminal may sometimes beconsidered as an infrastructure unit, for example if it relays data ortransmissions from other terminals to a base station (directly orindirectly). This term can thus include a base station for a macrocell,a base station for a small cell, a femtocell, a picocell, a relay node(operating in uplink and/or downlink), a terminal providing connectivityto one or more further terminals, etc.

As used herein, transmitting information or a message to an element mayinvolve sending one or more messages to the element and may involvesending part of the information separately from the rest of theinformation. The number of “messages” involved may also vary dependingon the layer or granularity considered.

In accordance with the present disclosure, when an uplink only relaynode relays uplink signals, it may transmit relayed signals to the basestation via one or more nodes (where the relayed signals are based onthe received first uplink signals). For example, the signals may betransmitted to the base station via one or more relay nodes where someor all of them may be operating in one of an uplink-only mode or anuplink-and-downlink mode.

It is noteworthy that even though the present disclosure has beendiscussed in the context of LTE, its teachings are applicable to but notlimited to LTE or to other 3GPP standards. In particular, even thoughthe terminology used herein is generally the same or similar to that ofthe LTE standards, the teachings are not limited to the present versionof LTE and could apply equally to any appropriate arrangement not basedon LTE and/or compliant with any other future version of an LTE or 3GPPor other standard.

Various further aspects and features of the present technique aredefined in the appended claims. Various modifications may be made to theembodiments hereinbefore described within the scope of the appendedclaims. For example although LTE has been presented as an exampleapplication, it will be appreciated that other mobile communicationssystems can be used for which the present technique can be used.

Various further aspects and features are defined in the followingnumbered paragraphs:

-   Paragraph 1. A mobile communications system comprising

a base station, the base station including a transmitter and a receiver,the transmitter being configured to transmit signals via a wirelessaccess interface to a plurality of relay nodes and to one or morecommunications terminals, and the receiver being configured to receivesignals via the wireless access interface from the plurality of relaynodes and from the one or more communications terminals, and

a controller operatively coupled to the base station and configured

to control a first relay node of the plurality relay nodes to transmitsignals representing the data to one of the communications terminalsreceived from the base station or to receive signals representing thedata from the communications terminal for transmission to the basestation, wherein,

upon first predetermined conditions being met, to control a second relaynode of the plurality of relay nodes to transmit signals representingthe data to the communications terminal received from the base stationor to receive signals representing the data from the communicationsterminal for transmission to the base station, and

to control the communications terminal to transmit a first signalrepresenting at least a first part of the data to the first relay nodefor transmission to the base station, and to transmit a second signalrepresenting at least a second part of the data to the second relay nodefor transmission to the base station.

-   Paragraph 2. A mobile communications system according to paragraph    1, wherein the controller is configured

upon second predetermined conditions being met, to control the secondrelay node not to transmit signals to the communications terminal andnot to receive signals from the communications terminal, such that thecommunications terminal is associated only with the first relay node,and

to control the communications terminal to transmit a signal representingthe data to the first relay node for transmission to the base station.

-   Paragraph 3. A mobile communications system according to paragraph 1    or 2, wherein the controller is configured to control the first    relay node to transmit signals to the communications terminal via a    first carrier signal and to receive signals from the communications    terminal via the first carrier signal and to control the second    relay node to transmit signals to the communications terminal via a    second carrier signal and to receive signals from the communications    terminal via the second carrier signal.-   Paragraph 4. A mobile communications system according to paragraphs    1 or 2, wherein the controller is configured to control the first    relay node to transmit signals to the communications terminal in    first communications resources and to receive signals from the    communications terminal in the first communications resources and to    control the second relay node to transmit signals to the    communications terminal in second communications resources and to    receive signals from the communications terminal in the second    communications resources.-   Paragraph 5. A mobile communications system according to paragraphs    1 or 2, wherein the controller is configured to assign a first    identifier to the first relay node and a second identifier to the    second relay node.-   Paragraph 6. A mobile communications system according to any of    paragraphs 1 to 5, wherein the first predetermined conditions    include an amount of data being transmitted or received by the first    relay node being above a predetermined threshold.-   Paragraph 7. A mobile communications system according to any of    paragraphs 1 to 6, wherein the first predetermined conditions    include an amount of power being consumed by the first relay node    being above a predetermined threshold.-   Paragraph 8. A mobile communications system according to any of    paragraphs 1 to 7, wherein the first predetermined conditions    include an indication that the difference between a first amount of    data being transmitted or received by the first relay node and a    second amount of data being transmitted or received by the second    relay node being above a predetermined threshold.-   Paragraph 9. A mobile communications system according to any of    paragraphs 1 to 8, wherein the first predetermined conditions    include an indication that a communications link between the second    relay node and the communications terminal and/or base station being    of a higher quality than a communications link between the first    relay node and the communications terminal and/or base station.-   Paragraph 10. A mobile communications system according to any of    paragraphs 1 to 9, wherein the second predetermined conditions    include an indication that an amount of data being transmitted or    received by the first relay node being below a predetermined    threshold.-   Paragraph 11. A mobile communications system according to any of    paragraphs 1 to 10, wherein the second predetermined conditions    include an indication that an amount of power being consumed by the    first relay node being below a predetermined threshold.-   Paragraph 12. A mobile communications system according to any of    paragraphs 1 to 11, wherein the second predetermined conditions    include an indication that the difference between a first amount of    data being transmitted or received by the first relay node and a    second amount of data being transmitted or received by the second    relay node being below a predetermined threshold.-   Paragraph 13. A mobile communications system according to any of    paragraphs 1 to 12, wherein the second predetermined conditions    include an indication that a communications link between the second    relay node and the communications terminal and/or base station being    of a lower quality than a communications link between the first    relay node and the communications terminal and/or base station.-   Paragraph 14. A mobile communications system according to any of    paragraphs 1 to 13, wherein the communications terminal is    configured to transmit a request message to the first relay node for    transmission to the base station.-   Paragraph 15. A mobile communications system according to any of    paragraphs 1 to 14, wherein the controller is configured

upon third predetermined conditions being met, to control a third relaynode of the plurality of relay nodes to transmit signals representingthe data to the communications terminal or to receive signalsrepresenting the data from the communications terminal, such that thecommunications terminal is associated with three of the plurality ofrelay nodes, and

to control the communications terminal to transmit a third signalrepresenting at least a third part of the data to the third relay nodefor transmission for the base station.

-   Paragraph 16. A method of operating a relay node in a mobile    communications system, the method comprising

receiving a first indication to transmit signals representing first datato a communications terminal, to one or more other relay nodes and to abase station, and to receive signals representing the first data fromthe communications terminal, to the one or more other relay nodes andthe base station, and

receiving a second indication to transmit signals representing seconddata to the one or more other relay nodes and to the base station, andto receive signals representing the second data to the one or more otherrelay nodes and to the base station.

-   Paragraph 17. A communications terminal forming part of a mobile    communications system, the communications terminal being configured

to transmit signals representing data to a first relay node of aplurality of relay nodes, and

upon predetermined conditions being met to transmit signals representingat least a first part of the data to the first relay node and totransmit signals representing at least a second part of the data to asecond relay node of the plurality of relay nodes.

-   Paragraph 18. A communications terminal according to paragraph 17,    where upon the predetermined conditions being met, the    communications terminal is configured to transmit a request message    to the first relay node.-   Paragraph 19. A communications terminal according to paragraph 17,    where upon the predetermined conditions being met, a controller is    configured to control the communications terminal to transmit    signals representing at least the second part of the data to the    second relay node.

REFERENCES

-   [1]3GPP TR36.872 V12.1.0, “Small cell enhancements for E-UTRA and    E-UTRAN—Physical Layer aspects”, December 2013.-   [2] Holma H. and Toskala A., “LTE for UMTS OFDMA and SC-FDMA Based    Radio Access”, John Wiley & Sons Limited, January 2010.

1. A mobile communications system comprising a base station, the basestation including a transmitter and a receiver, the transmitter beingconfigured to transmit signals via a wireless access interface to aplurality of relay nodes and to one or more communications terminals,and the receiver being configured to receive signals via the wirelessaccess interface from the plurality of relay nodes and from the one ormore communications terminals, and a controller operatively coupled tothe base station and configured to control a first relay node of theplurality relay nodes to transmit signals representing the data to oneof the communications terminals received from the base station or toreceive signals representing the data from the communications terminalfor transmission to the base station, wherein, upon first predeterminedconditions being met, to control a second relay node of the plurality ofrelay nodes to transmit signals representing the data to thecommunications terminal received from the base station or to receivesignals representing the data from the communications terminal fortransmission to the base station, and to control the communicationsterminal to transmit a first signal representing at least a first partof the data to the first relay node for transmission to the basestation, and to transmit a second signal representing at least a secondpart of the data to the second relay node for transmission to the basestation.
 2. A mobile communications system as claimed in claim 1,wherein the controller is configured upon second predeterminedconditions being met, to control the second relay node not to transmitsignals to the communications terminal and not to receive signals fromthe communications terminal, such that the communications terminal isassociated only with the first relay node, and to control thecommunications terminal to transmit a signal representing the data tothe first relay node for transmission to the base station.
 3. A mobilecommunications system as claimed in claim 1, wherein the controller isconfigured to control the first relay node to transmit signals to thecommunications terminal via a first carrier signal and to receivesignals from the communications terminal via the first carrier signaland to control the second relay node to transmit signals to thecommunications terminal via a second carrier signal and to receivesignals from the communications terminal via the second carrier signal.4. A mobile communications system as claimed in claim 1, wherein thecontroller is configured to control the first relay node to transmitsignals to the communications terminal in first communications resourcesand to receive signals from the communications terminal in the firstcommunications resources and to control the second relay node totransmit signals to the communications terminal in second communicationsresources and to receive signals from the communications terminal in thesecond communications resources.
 5. A mobile communications system asclaimed in claim 1, wherein the controller is configured to assign afirst identifier to the first relay node and a second identifier to thesecond relay node.
 6. A mobile communications system as claimed in claim1, wherein the first predetermined conditions include an amount of databeing transmitted or received by the first relay node being above apredetermined threshold.
 7. A mobile communications system as claimed inclaim 1, wherein the first predetermined conditions include an amount ofpower being consumed by the first relay node being above a predeterminedthreshold.
 8. A mobile communications system as claimed in claim 1,wherein the first predetermined conditions include an indication thatthe difference between a first amount of data being transmitted orreceived by the first relay node and a second amount of data beingtransmitted or received by the second relay node being above apredetermined threshold.
 9. A mobile communications system as claimed inclaim 1, wherein the first predetermined conditions include anindication that a communications link between the second relay node andthe communications terminal and/or base station being of a higherquality than a communications link between the first relay node and thecommunications terminal and/or base station.
 10. A mobile communicationssystem as claimed in claim 2, wherein the second predeterminedconditions include an indication that an amount of data beingtransmitted or received by the first relay node being below apredetermined threshold.
 11. A mobile communications system as claimedin claim 2, wherein the second predetermined conditions include anindication that an amount of power being consumed by the first relaynode being below a predetermined threshold.
 12. A mobile communicationssystem as claimed in claim 2, wherein the second predeterminedconditions include an indication that the difference between a firstamount of data being transmitted or received by the first relay node anda second amount of data being transmitted or received by the secondrelay node being below a predetermined threshold.
 13. A mobilecommunications system as claimed in claim 2, wherein the secondpredetermined conditions include an indication that a communicationslink between the second relay node and the communications terminaland/or base station being of a lower quality than a communications linkbetween the first relay node and the communications terminal and/or basestation.
 14. A mobile communications system as claimed in claim 1wherein the communications terminal is configured to transmit a requestmessage to the first relay node for transmission to the base station.15. A mobile communications system as claimed in claim 1, wherein thecontroller is configured upon third predetermined conditions being met,to control a third relay node of the plurality of relay nodes totransmit signals representing the data to the communications terminal orto receive signals representing the data from the communicationsterminal, such that the communications terminal is associated with threeof the plurality of relay nodes, and to control the communicationsterminal to transmit a third signal representing at least a third partof the data to the third relay node for transmission for the basestation. 16-20. (canceled)
 21. A communications terminal forming part ofa mobile communications system, the communications terminal beingconfigured to transmit signals representing data to a first relay nodeof a plurality of relay nodes, and upon predetermined conditions beingmet to transmit signals representing at least a first part of the datato the first relay node and to transmit signals representing at least asecond part of the data to a second relay node of the plurality of relaynodes.
 22. A communications terminal as claimed in claim 21, where uponthe predetermined conditions being met, the communications terminal isconfigured to transmit a request message to the first relay node.
 23. Acommunications terminal as claimed in claim 21, where upon thepredetermined conditions being met, a controller is configured tocontrol the communications terminal to transmit signals representing atleast the second part of the data to the second relay node.
 24. A methodof operating a communications terminal in a mobile communicationssystem, the method comprising transmitting signals representing data toa first relay node of a plurality of relay nodes, and upon predeterminedconditions being met transmitting signals representing at least a firstpart of the data to the first relay node and transmitting signalsrepresenting at least a second part of the data to a second relay nodeof the plurality of relay nodes.
 25. (canceled)